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Biology 2nd Baccalaureate

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13.1. Ecosystem components

Ecosystem components

The ecosystem

Before defining what an ecosystem is, we must remember that a system is a set of elements that are related to each other to perform some function that they could not perform if it were not with the collaboration of the other components.

Therefore, a system is made up of a series of elements that make up the parts of the system and the relationships that occur between these elements. Its operation involves an expenditure of matter and energy.

Therefore, an ecosystem is the set formed by the physical environment (abiotic components, the biotope), by the organisms that live in it (biotic components, the biocenosis or community), and by the relationships that are established between all its components and the environment in which they live.

For example, the lake is an aquatic ecosystem of freshwater more or less transparent, they live algae, aquatic plants, insects, worms, etc. The steppe is another ecosystem characterized grow on poor soils and aggregates, in living plants and animals adapted to this environment, such as thyme, rosemary, hare, lizards, etc.

El ecosistema está formado por el biotopo y la biocenosis

Tomado de José Alberto Bermúdez bajo Licencia Creative Commons Atribución 4.0 Internacional.

Ecosystems can be of very different sizes, from the size of a decomposing log, to that of a pond, or that of a forest or an island.

The ecology is the branch of biology that studies ecosystems.

Interactive activity: Operation of the "beehive" system.

Game: Space eco-voyage.


The biotope is the place or physical environment in which living beings in an ecosystem live. It includes a substrate (soilwaterairrocks, etc.) and the physical and chemical conditions of that medium (temperature, humidity, luminosity, etc.).

The main environmental factors that determine the physical and chemical characteristics of the biotope are:

  • The light. The photosynthetic beings need light and it depends on the situation in the ecosystem.
  • The water. It is needed by all organisms, some require a lot of humidity, others less.
  • Temperature. There are beings that need warmer temperatures and others that are colder.
  • The salinity of the water. Depending on the concentration of dissolved salts in the water, there are organisms that can live in freshsalty or brackish water.
  • The pH. It is the degree of acidity or basicity of the medium.

There is a balance between all the environmental factors that condition the ecosystem, and if one of them varies, the other factors are also affected. For example, if there is a prolonged drought, the soil is not as fertile. 

Two different media can be distinguished that characterize the biotope:

  • Terrestrial environment. Characterized by the type of soil, degree of humidity, air temperature, amount of light, the substrate on which the organism sits. 
  • Aquatic environment. Characterized by the degree of salinity of the water (fresh, salty, brackish), by its transparency and luminosity, temperature, amount of gases and dissolved nutrients.

There are other terms used in ecology that can confuse us and that we should know that they are not synonymous with biotope.

  • Habitat: it is very similar to a biotope, but while the biotope refers to the environment in which the organisms of the ecosystem live (biological community), the habitat refers only to the environment in which an organism or population lives.
  • Ecological niche: it does not refer to a physical space, but to the role or function that an organism plays in the community and its position according to environmental conditions (temperature, pH, humidity, etc.). It could be said that it is the "trade" of a species within the ecosystem. That is, how they feed, hunt, avoid being hunted, compete, etc., with other members of the ecosystem. Therefore, the ecological niche includes environmental conditions (abiotic factors) and the influence of other species in their life (biotic factors).

The ecological niche that each species occupies is the result of interspecific competition that displaces species to occupy different sites. For example, we can see it when the exotic species that are introduced into an ecosystem displace the native species to more restricted niches.

For example: The field rat (Rattus rattus) has a wide niche, being able to live in a wide range of environmental factors (biotic and abiotic). In the 18th century, the sewer rat (Rattus novergicus) was introduced, with a more specific niche, specialized to live in a more humid environment and with less light, thus displacing the field rat from the sewers .

If a species has a small ecological niche width, it is a highly specialized species under these conditions and can displace other less specialized species to occupy other niches.

Biocenosis or community

The biocenosis or biotic community of an ecosystem is the set of all living beings that live in the biotope, among which certain relationships are established.

population is the set of individuals of the same species that live in a certain place. Living together allows them to feed, defend themselves, reproduce, etc. in better conditions than if they lived in isolation. For example, the population of mallards in a lake.

Therefore, the biocenosis is formed by the set of populations that live in the same place and that are related to each other.

Group activity: Modeling food webs in Darién, Panama.

Answer in your notebook

13.1.- What differences are there between the biotope and the biocenosis?


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.